As is known, generally gas turbine engines comprise a compressor section, a combustion chamber, and a turbine section. In general, the compressor section draws in air and compresses it. Fuel is then added to the compressed air in the combustion chamber, and the mixed fluid of fuel and compressed air is ignited. The fluid, which is at a temperature in the range of about 1700-2600 degrees Fahrenheit after ignition, is directed toward the turbine section where part of the energy in the fluid is extracted by the turbine blades which are mounted to a rotatable shaft. The rotating shaft in turn drives a compressor in the compressor section. The remainder of the energy is used for other functions; for example, the propulsive thrust of a jet aircraft.
To better improve the efficiency of the energy transfer from the fluid to the turbine blades, the angle of attack of the fluid onto the turbine blades is improved by use of non-rotating airfoil shaped fluid nozzles or vanes. These nozzles or vanes swirl the flow of the hot gas or fluid from a nearly parallel flow with the blades to a generally circumferential flow onto the blades. Because the combusted fluid is at a very high temperature when it comes in contact with the vane, the vane must be designed to withstand high temperatures for long periods of time.
Conventional gas turbine nozzles or vanes are generally internally cooled by pumping a portion of the compressed air through an internal cooling cavity in the vane. However, the cooling cavities currently known in the art are designed for high pressure drop, high velocity air flow systems and will not effectively cool nozzles used in low pressure ratio engines. For example, most vanes are designed to operate in machines that have a differential pressure of about 40-80 psi. Examples of the conventional prior art include U.S. Pat. Nos. 3,574,481 to Pyne Jr. entitled "Variable Area Cooled Airfoil Construction for Gas Turbines," 4,105,364 to Dodd entitled "Vane for a Gas Turbine Engine Having Means for Impingement Cooling Thereof," 4,278,400 to Yamarik et al. entitled "Coolable Rotor Blade," 4,403,917 to Laffitte et al. entitled "Turbine Distributor Vane," 4,456,428 to Cuvillier entitled "Apparatus for Cooling Turbine Blades," 4,515,523 to North et al. entitled "Cooling Arrangement for Airfoil Stator Vane Trailing Edge," 5,288,207 to Linask entitled "Internally Cooled Turbine Airfoil," 5,337,805 to Green et al. entitled "Airfoil Core Trailing Edge Region," and 5,342,172 to Coudray et al. entitled "Cooled Turbo-Machine Vane."
As will be appreciated, there thus exists a need for a turbine vane that can be internally cooled when used in a low pressure ratio engine; for example, about a 3 psi pressure differential.